The present invention relates to a device that allows elements in the form of sheets to be printed by hot stamping.
The invention finds a particularly advantageous, although not exclusive, application in the field of packaging for luxury goods.
It is known practice for texts and/or patterns to be printed by hot stamping, that is to say for colored or metallized film from one or more stamping strips to be applied under pressure to a support in the form of a sheet. In industry, such a transfer operation is usually performed using a vertical platen press, into which the supports for printing are introduced sheet by sheet, while the stamping strips are fed continuously.
In a standard platen press, stamping is performed between a horizontally fixed platen and a platen that is mounted such that it can move in a reciprocating vertical movement. Because this type of press is generally automated, transport means are provided to bring each sheet between the platens one by one. In practice, this is usually a series of gripper bars each of which in turn takes hold of a sheet at the front edge thereof, before pulling it in between the two platens when the latter are sufficiently parted.
This type of device does, however, have the disadvantage of guaranteeing high print quality only at low production rates, given that a crumpling phenomenon arises as soon as the stamping rate becomes too high. In its deceleration movement before it comes to a standstill between the two platens of the press, the rear portion of the sheet in fact has a tendency to catch up with the front portion carried by the gripper bar. This has the effect of appreciably disrupting the flatness of the sheet, accordingly increasing the risk of its becoming crumpled as the moving platen comes to press against the fixed platen.
One idea that has been considered, in an attempt to overcome this difficulty, is to use a blower to keep the sheet roughly flat as it comes to a standstill between the two platens of the press. The idea is for this blower to be positioned downstream of the press and for its jet of pressurized air to be directed in the plane of the sheet, so as to slow it during the deceleration phase. Be that as it may, while such an arrangement does actually allow the stamping rate to be increased, it does nonetheless also have its own limits.
Hence, the technical problem addressed by the subject matter of the invention is that of providing a printing device for printing elements in the form of sheets, comprising, on the one hand, a platen press able by hot stamping to affix to each sheet colored or metallized film from at least one stamping strip and, on the other hand, transport means able to introduce each sheet one after the other into the platen press by pulling said sheet by its front edge, which printing device would make it possible to avoid the problems of the prior art while notably offering an appreciably higher production rate.